1. Field of the Invention
The present invention relates to a three-dimensional (3D) display device, and in particular, to an autostereoscopy-type 3D display device using a parallax barrier.
2. Description of Related Art
Generally, 3D displays supply different views to the left and right eyes of a user such that the user can have the depth perception of the viewing images. Autostereoscopic displays are 3D displays with which the user can see a desired 3D image without wearing viewing aids, such as polarized glasses.
A common autostereoscopic display utilizes an optical separation element (or optical isolation element), such as a lenticular lens, a parallax barrier or a microlens array, to spatially separate or isolate the left-eye image part and the right-eye image part displayed at the image display unit in the directions of the left and right eyes of the user, respectively. For example, the parallax barrier may be formed with a liquid crystal shutter utilizing a transmission type liquid crystal display, and in this case, it may be converted between a 2D mode and a 3D mode.
FIG. 8 is a partial sectional view of a conventional 3D display device using a parallax barrier. In relation to such a structure, U.S. Pat. No. 6,040,807 discloses a 3D display device using a parallax barrier.
First pixels 3a corresponding to the left-eye images and second pixels 3b corresponding to the right-eye images are alternately and repeatedly arranged at an image display unit 1 in a horizontal direction of the screen, and a parallax barrier 5 is placed in front of the image display unit 1. Light interception portions 7 and light transmission portions 9 are alternately and repeatedly arranged at the parallax barrier 5 in the horizontal direction (i.e., X-axis direction) of the screen.
With the above structure, the left-eye image light beams emitted from the first pixels 3a are transmitted through the light transmission portions 9 toward the left eye of the viewer (L1) while being intercepted by the light interception portions 7 in the direction of the right eye of the viewer (L2). The right-eye image light beams emitted from the second pixels 3b are transmitted through the light transmission portions 9 toward the right eye of the viewer (R1) while being intercepted by the light interception portions 7 in the direction of the left eye of the viewer (R2). Accordingly, the left and right images respectively reach the left and right eyes so that the user or viewer can see the desired 3D images.
With the above-structured 3D display device, the visual range R′, in which the viewer can view the 3D images, is defined by the following Equation 1:
                              R          ′                =                  re                      L            ′                                              (                  Eq          .                                          ⁢          1                )            where r indicates a distance between the image formation plane of the image display unit 1 and an image separation plane (or an image isolation plane) of the parallax barrier 5 (referred to hereinafter as a distance between the image formation plane and the image separation plane), e is an image separation distance between the left-eye image and the right-eye image separated by the parallax barrier 5, and L′ is a pixel pitch of the image display unit 1. The image separation distance e is established to be the distance between the left and right eyes of the viewer, which is usually assumed to be 65 mm.
It is assumed in Equation 1 that the refraction index of all media which exist on the route of the light emitted from the image display unit 1 is 1. As the refraction index of the respective media is typically not 1, the route of the light should be corrected using the Snell's law of refraction.
It can be seen from Equation 1 that the visual range R′ depends on the distance r between the image formation and image separation planes.
When the image display unit 1 is formed with a liquid crystal display, it becomes difficult to reduce the distance r between the image formation and image separation planes to be 0.6 mm or less because of the thickness of the front substrate of the liquid crystal display (about 0.5 mm) and the thickness of the polarizing plate (about 0.1 mm) attached to the front surface of the front substrate. Moreover, when the parallax barrier 5 is formed with a liquid crystal shutter, the distance r between the image formation and image separation planes exceeds about 1.0 mm with the addition of the thickness of the rear substrate of the liquid crystal shutter (about 0.3 mm or more). Accordingly, the 3D display device using the parallax barrier 5 has a visual range R′ of at least a certain minimum value.
For instance, the visual range R′ of the 3D display device can be described in the following way.
For example, in a 3D display device, suppose the pixel pitch L′ of the image display unit 1 is 47 μm, and the width M of each of the pixels arranged at the image display unit 1 is 29 μm. The distance r between the image formation and image separation planes is established to be 0.6 mm. Under this condition, the left-eye image and the right-eye image are separated from each other in correspondence with the distance between the left and right eyes, and hence, it turns out that the visual range R′ for viewing the 3D images is about 830 mm, assuming that the image separation distance e=65 mm.
However, when the refraction index of the front substrate provided at the image display unit 1 is assumed to be 1.5, and the Snell's law is applied, the distance at which the left-eye image light beam L1 and the right-eye image light beam R1 are separated in correspondence with the distance between the left and the right eyes, that is, the visual range R′, is about 540 mm.
Even then, the visual range of 540 mm with the conventional 3D display device is too large to be used in a mobile device, such as a cellular phone. This is because most of the users see the screen within the distance of about 300 mm when using the mobile device. Moreover, in case the parallax barrier 5 is formed with a liquid crystal shutter, the visual range becomes even greater. Accordingly, it is difficult to use the conventional 3D display device for the mobile device because of a large visual range R′.